I am interpreting your post to say "how can I convert mp4 to data file so I can burn it to play in dvd".
I'm hoping you're not actual after .dat files, because many different programs use them, and each is specific to the program that makes them.
.dat files can be made by VCDGear, and played as a video cd, but this is uncommon.
So, you can convert an mp4 video file with DVDFlick or FAVC to play in a dvd player. This takes it to dvd-video format and can be burned on a blank dvd.
If you have a player that is capable of playing mpg4 or avi file encoded with divx or xvid, you can just burn the video onto a blank disk as data...like any other normal file. You need to check your original video and see what codecs were used to make it. To do this, open it with MediaInfo or Gspot video utility.